[PATCH] drm/aperture: Run fbdev removal before internal helpers

[Thomas Zimmermann]

Always run fbdev removal first to remove simpledrm via
sysfb_disable(). This clears the internal state. The later call
to drm_aperture_detach_drivers() then does nothing. Otherwise,
with drm_aperture_detach_drivers() running first, the call to
sysfb_disable() uses inconsistent state.

Example backtrace show below:

[   11.663422] ==================================================================
[   11.663426] BUG: KASAN: use-after-free in device_del+0x79/0x5f0
[   11.663435] Read of size 8 at addr ffff888108185050 by task systemd-udevd/311
[   11.663440] CPU: 0 PID: 311 Comm: systemd-udevd Tainted: G            E     5
	.19.0-rc2-1-default+ #1689
[   11.663445] Hardware name: HP ProLiant DL120 G7, BIOS J01 04/21/2011
[   11.663447] Call Trace:
[   11.663449]  <TASK>
[   11.663451]  ? device_del+0x79/0x5f0
[   11.663456]  dump_stack_lvl+0x5b/0x73
[   11.663462]  print_address_description.constprop.0+0x1f/0x1b0
[   11.663468]  ? device_del+0x79/0x5f0
[   11.663471]  ? device_del+0x79/0x5f0
[   11.663475]  print_report.cold+0x3c/0x21c
[   11.663481]  ? lock_acquired+0x87/0x1e0
[   11.663484]  ? lock_acquired+0x87/0x1e0
[   11.663489]  ? device_del+0x79/0x5f0
[   11.663492]  kasan_report+0xbf/0xf0
[   11.663498]  ? device_del+0x79/0x5f0
[   11.663503]  device_del+0x79/0x5f0
[   11.663509]  ? device_remove_attrs+0x170/0x170
[   11.663514]  ? lock_is_held_type+0xe8/0x140
[   11.663523]  platform_device_del.part.0+0x19/0xe0
[   11.663530]  platform_device_unregister+0x1c/0x30
[   11.663535]  sysfb_disable+0x2d/0x70
[   11.663540]  remove_conflicting_framebuffers+0x1c/0xf0
[   11.663546]  remove_conflicting_pci_framebuffers+0x130/0x1a0
[   11.663554]  drm_aperture_remove_conflicting_pci_framebuffers+0x86/0xb0
[   11.663561]  ? mgag200_pci_remove+0x30/0x30 [mgag200]
[   11.663578]  mgag200_pci_probe+0x2d/0x140 [mgag200]

Signed-off-by: Thomas Zimmermann <tzimmermann at suse.de>
Fixes: 873eb3b11860 ("fbdev: Disable sysfb device registration when removing conflicting FBs")
Cc: Javier Martinez Canillas <javierm at redhat.com>
Cc: Daniel Vetter <daniel.vetter at ffwll.ch>
Cc: Daniel Vetter <daniel at ffwll.ch>
Cc: Sam Ravnborg <sam at ravnborg.org>
Cc: Helge Deller <deller at gmx.de>
Cc: Thomas Zimmermann <tzimmermann at suse.de>
Cc: Alex Deucher <alexander.deucher at amd.com>
Cc: Zhen Lei <thunder.leizhen at huawei.com>
Cc: Changcheng Deng <deng.changcheng at zte.com.cn>
---
 drivers/gpu/drm/drm_aperture.c | 26 +++++++++++++++-----------
 1 file changed, 15 insertions(+), 11 deletions(-)

diff --git a/drivers/gpu/drm/drm_aperture.c b/drivers/gpu/drm/drm_aperture.c
index 74bd4a76b253..059fd71424f6 100644
--- a/drivers/gpu/drm/drm_aperture.c
+++ b/drivers/gpu/drm/drm_aperture.c
@@ -329,7 +329,20 @@ int drm_aperture_remove_conflicting_pci_framebuffers(struct pci_dev *pdev,
 						     const struct drm_driver *req_driver)
 {
 	resource_size_t base, size;
-	int bar, ret = 0;
+	int bar, ret;
+
+	/*
+	 * WARNING: Apparently we must kick fbdev drivers before vgacon,
+	 * otherwise the vga fbdev driver falls over.
+	 */
+#if IS_REACHABLE(CONFIG_FB)
+	ret = remove_conflicting_pci_framebuffers(pdev, req_driver->name);
+	if (ret)
+		return ret;
+#endif
+	ret = vga_remove_vgacon(pdev);
+	if (ret)
+		return ret;
 
 	for (bar = 0; bar < PCI_STD_NUM_BARS; ++bar) {
 		if (!(pci_resource_flags(pdev, bar) & IORESOURCE_MEM))
@@ -339,15 +352,6 @@ int drm_aperture_remove_conflicting_pci_framebuffers(struct pci_dev *pdev,
 		drm_aperture_detach_drivers(base, size);
 	}
 
-	/*
-	 * WARNING: Apparently we must kick fbdev drivers before vgacon,
-	 * otherwise the vga fbdev driver falls over.
-	 */
-#if IS_REACHABLE(CONFIG_FB)
-	ret = remove_conflicting_pci_framebuffers(pdev, req_driver->name);
-#endif
-	if (ret == 0)
-		ret = vga_remove_vgacon(pdev);
-	return ret;
+	return 0;
 }
 EXPORT_SYMBOL(drm_aperture_remove_conflicting_pci_framebuffers);
-- 
2.36.1